arXiv subjects

E. M. Rossi

Publications and source records attributed to E. M. Rossi.

23 records · Page 2Linked to original sources

arXiv2009

The Growth of Supermassive Black Holes Across Cosmic Time

One of the main themes in extragalactic astronomy for the next decade will be the evolution of galaxies over cosmic time. Many future observatories, including JWST, ALMA, GMT, TMT and E-ELT will intensively observe starlight over a broad redshift range, out to the dawn of the modern Universe when the first galaxies formed. It has, however, become clear that the properties and evolution of galaxies are intimately linked to the growth of their central black holes. Understanding the formation of galaxies, and their subsequent evolution, will therefore be incomplete without similarly intensive observations of the accretion light from supermassive black holes (SMBH) in galactic nuclei. To make further progress, we need to chart the formation of typical SMBH at z>6, and their subsequent growth over cosmic time, which is most effectively achieved with X-ray observations. Recent technological developments in X-ray optics and instrumentation now bring this within our grasp, enabling capabilities fully matched to those expected from flagship observatories at longer wavelengths.

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arXiv2006

Properties of X-Ray Rich Gamma Ray Bursts and X-Ray Flashes detected with BeppoSAX and Hete-2

We study the spectrum of the prompt emission and the X-ray and optical afterglow fluxes of 54 X-Ray Rich Gamma Ray Burst (XRRs) and X-Ray Flashes (XRFs), observed by BeppoSax and HETE-2. A comparison is then performed with classical Gamma Ray Bursts (GRBs). The goal of this paper is to investigate the nature of XRRs/XRFs, as high redshift GRBs or off-axis GRBs, analyzing both their prompt and afterglow properties. We find that the XRR/XRF spectral indexes of the Band function are similar to those of classical GRBs, whereas the peak energy is lower by a factor of 4. We study the optical and X-Ray afterglow properties of the XRRs/XRFs; in particular we analyze the XRR 011030 afterglow. We find that the X-ray and optical flux distributions and the lightcurves of the XRRs/XRFs sample are consistent with those of classical GRBs; in particular, they show evidence of a break and no rising temporal slope. We compare these results with the afterglow predictions of the high redshift scenario, where XRFs are GRBs at higher redshift and of the off-axis scenario, where the observed differences are due to viewing angle effects. In this last framework, we consider jets with a homogeneous, a -2 power-law shaped and a Gaussian luminosity angular distribution. We find that the high redshift scenario can explain some events but not the total sample of XRRs/XRFs. The off-axis model may be consistent with our findings when a homogeneous jet is considered. However, given the uncertainties on the selection effects in our sample, a Gaussian jet viewed at small angles from the Gaussian core and a power-law shaped cannot be ruled out.

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arXiv2006

The redshift distribution of SWIFT Gamma-Ray Bursts: evidence for evolution

We predict the redshift distribution of long Gamma-Ray Bursts (GRBs) with Monte Carlo simulations. Our improved analysis constrains free parameters with three kinds of observation: (i) the log(N)-log(P) diagram of BATSE bursts; (ii) the peak energy distribution of bright BATSE bursts; (iii) the HETE2 fraction of X-ray rich GRBs and X-ray flashes. The statistical analysis of the Monte Carlo simulation results allow us to carefully study the impact of the uncertainties in the GRB intrinsic properties on the redshift distribution. The comparison with SWIFT data then leads to the following conclusions. The Amati relation should be intrinsic, if observationally confirmed by SWIFT. The progenitor and/or the GRB properties have to evolve to reproduce the high mean redshift of SWIFT bursts. Our results favor an evolution of the efficiency of GRB production by massive stars, that would be ~6-7 times higher at z~7 than at z~2. We finally predict around 10 GRBs detected by SWIFT at redshift z>6 for a three year mission. These may be sufficient to open a new observational window over the high redshift Universe.

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arXiv2005

Open issues in gamma-ray bursts: polarimetry and dark GRBs

We review some open problems in the physics of afterglows, namely their polarization properties and the existence of dark/faint bursts. Polarization studies yield precious insights in the physical structure and dynamical evolution of GRB jets, revealing their magnetization properties and their energy profile. Polarimetric observations of GRB 020813 already allowed to exclude a homogeneous jet for this event. We then present observations of faint/dark bursts, showing that some of them may be obscured by dust, while others are possibly just intrinsically dim.

astro-ph↗

arXiv2002

Emission lines in GRBs constrain the total energy reservoir

The emission features observed in the X-ray afterglow of Gamma Ray Bursts are extremely powerful. Since they last at least for several hours, they imply energies of the order of 1e49 ergs. This in turn implies that the energy contained in the illuminating continuum thought to be responsible of the line production must exceed 1e51 ergs. This is a strong lower limit to the energy reservoir of Gamma Ray Bursts, which is independent of collimation and beaming, and bears important consequences on the possible collimation of the fireball radiation and the density of the medium surrounding the burst.

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